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900. Stream move-assignment

Section: 31.10.4 [ifstream] Status: C++11 Submitter: Niels Dekker Opened: 2008-09-20 Last modified: 2023-02-07

Priority: Not Prioritized

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Discussion:

It appears that we have an issue similar to issue 675(i) regarding the move-assignment of stream types. For example, when assigning to an std::ifstream, ifstream1, it seems preferable to close the file originally held by ifstream1: 

ifstream1 = std::move(ifstream2);

The current Draft (N2723) specifies that the move-assignment of stream types like ifstream has the same effect as a swap:

Assign and swap [ifstream.assign] 

basic_ifstream& operator=(basic_ifstream&& rhs);

Effects: swap(rhs).

[ Batavia (2009-05): ]

Howard agrees with the analysis and the direction proposed.

Move to Open pending specific wording to be supplied by Howard.

[ 2009-07 Frankfurt: ]

Howard is going to write wording.

[ 2009-07-26 Howard provided wording. ]

[ 2009-09-13 Niels adds: ]

Note: The proposed change of 31.10.3.3 [filebuf.assign] p1 depends on the resolution of LWG 1204(i), which allows implementations to assume that *this and rhs refer to different objects.

[ 2009 Santa Cruz: ]

Leave as Open. Too closely related to 911(i) to move on at this time.

[ 2010 Pittsburgh: ]

Moved to Ready for Pittsburgh.

Proposed resolution:

Change 31.8.2.3 [stringbuf.assign]/1: 

basic_stringbuf& operator=(basic_stringbuf&& rhs);

-1- Effects: swap(rhs).

Change [istringstream.assign]/1: 

basic_istringstream& operator=(basic_istringstream&& rhs);

-1- Effects: swap(rhs).

Change [ostringstream.assign]/1: 

basic_ostringstream& operator=(basic_ostringstream&& rhs);

-1- Effects: swap(rhs).

Change [stringstream.assign]/1: 

basic_stringstream& operator=(basic_stringstream&& rhs);

-1- Effects: swap(rhs).

Change 31.10.3.3 [filebuf.assign]/1: 

basic_filebuf& operator=(basic_filebuf&& rhs);

-1- Effects: swap(rhs).

Change [ifstream.assign]/1: 

basic_ifstream& operator=(basic_ifstream&& rhs);

-1- Effects: swap(rhs).

Change [ofstream.assign]/1: 

basic_ofstream& operator=(basic_ofstream&& rhs);

-1- Effects: swap(rhs).

Change [fstream.assign]/1: 

basic_fstream& operator=(basic_fstream&& rhs);

-1- Effects: swap(rhs).